Most of the time the courts are interested in the welfare of the children above other considerations.
They go with the odds and give custody to Mothers more often and demand child support from men more often.
When the woman involved is the less responsible parent or the man involved is earning little money this idea fails , but I think that the courts are aware of what is the more common situation.
I don't think the court has got the time to really find the truth, so they make the rules that succeed more often than fail.